1. Field of the Invention
The invention relates to woodworking tools generally. In particular the invention provides an inexpensive device and method for working within a confined space to accurately rout curved work pieces of large radius. The invention may also be used to draw full-scale layouts.
2. Description of the Related Art
Methods of routing curved work pieces and of producing full-scale layouts are well known. However, when working with large radii these methods are either inconvenient because they require a large work space and waste a great deal of material, or very expensive.
One method for routing at large radii is to use a CNC (Computer Numerical Control) machine. This type of machine is capable of working with pieces of very large radius while producing very accurate results. The principal drawback to this machine however is that it is very expensive, costing upwards of $100,000. Furthermore, farming the work out to a bigger shop that owns a CNC machine is also prohibitively expensive, costing $200 or more depending on the size and type of the order. Due to the nature of the construction industry, where work projects are awarded to the lowest bidder, it is critical to keep costs down as much as possible. A subcontractor who uses a CNC machine often will not be the low bidder.
An inexpensive method of both routing at large radii and producing full-scale layouts is to use a trammel. This device is simply a long arm that is rotatably fixed at one end and adapted to mount a router or marking instrument on the other end. U.S. Pat. Nos. 4,685,496 and 5,486,076 disclose trammels for mounting a router. The length of the trammel arm corresponds to the radius of the work piece. The trammel is pivotally secured at a point on the trammel spaced from the router, and the trammel acts as a guide to allow the router to trace a circumference on the work piece.
This method has a number of drawbacks. First, because the trammel arm must be the same length as the radius of the work piece, very large work spaces are needed to work with the trammel when routing large radii. Floor space in a workshop is of course very valuable. Therefore it is not practical for most shops to devote a large section of the shop floor to routing large radius pieces. Nor is it practical for the shop to spend the time necessary to clear an area for this operation. The space is better suited for ongoing projects.
Second, constructing a long trammel requires a great deal of material and requires a significant number of man-hours. Furthermore, trammels of various lengths must be built to meet the needs of each job. If a new trammel is to be built for each job, a significant cost in materials and man-hours must be absorbed. Conversely, if a number of trammels of different lengths are to be built and stored for future use, costs in wasted storage space arise.
Third, trammels over twenty feet long require two workers to operate, and the results are generally of poor quality. Long trammels tend to flex during operation, which results in flat spots being formed along the circumference of the work piece.
Trammels may also be used to produce full-scale layouts. However, the same difficulties described above in connection with routing must be overcome. Another known method of producing full-scale layouts that solves these problems is to use a computer and CAD (computer-aided design) software. The layout is drawn on the computer screen and then put on paper using a plotter. This method produces very high quality results, but requires a large and expensive investment to purchase the necessary hardware and software.
U.S. Pat. No. 3,393,453 discloses a device for scribing large radii on layouts that overcomes some of the problems outlined above in connection with trammels. The device uses a trammel in combination with a template to produce large radii without the need to use a correspondingly large trammel.
The device of the ""453 patent suffers from three principal drawbacks. First, the template is not adapted to be secured to a work surface during use. The operator must hold the template in place, where it is obviously prone to shift and produce poor quality arcs.
Second, the device may only be used to produce a limited range of arc radii, depending on what size templates are available. The carriage is adapted to ride on only a specific type of template, and this template is not readily producible by the average person.
Third, the invention may only be used to draw layouts. The trammel is not adapted to mount a router or other power tool.
Therefore, a device and method of routing at large radii and producing full-scale layouts that is inexpensive, easy for one person to use, and produces high quality results would be of great benefit in the woodworking industry.
The invention provides an apparatus and method for routing radii and for producing full scale layouts. The device is particularly well-adapted to work with large radii, because it is usable within confined spaces and requires only one person to operate, but produces exceptional results.
The device comprises a plurality of guides, a carriage assembly and an adjustable trammel arm. The guide is a curved section of material that is secured to a flat work surface. The radius of the guide is determined by the radius of the work piece, as discussed below. In operation, the guide steers the carriage as the carriage travels along a length of the guide.
The carriage assembly comprises a substantially rectangular support frame with four rotating members on its underside. The rotating members provide a low-friction interface between the guide and carriage as the carriage rides from one end of the guide to the other.
The trammel arm is adjustably secured to the carriage so that it defines an extension of the guide radius. In this orientation, the trammel is adjustable so that the sum of the trammel extension and the guide radius is equal to the radius of the work piece or layout. The end of the trammel opposite the carriage is adapted to mount a router for cutting or a marking instrument for drawing. Other types of power tools may be mounted to the trammel arm, such as jigsaws or circular saws, but routers are preferred to produce the highest quality finished product.
To practice the method of using the apparatus, first an appropriately sized guide is secured to the work surface. Second, the carriage is positioned atop the guide and secured in place. Third, a router or marking instrument is secured to the trammel. Fourth, the work piece or layout is secured to the work surface at the appropriate distance from the guide. Fifth, measurements are made and the trammel arm is adjusted to the appropriate length and secured into place. Finally, the arc is drawn or the work piece is routed by moving the carriage along the guide.